Now it looks like that the ReadExcel & ReadCSV infer the data type (metadata) by looking at the first records. This is a problem in my case since some times I have lots of data that only changes after a while. This results in RapidMiner thinking that an attribute was binominal while it is polynominal. I can then fix it by hand but it will be much easier to have the option of specifying how many lines it should read to infer metadata and having as default the current settings.